The discussion of the background of the invention herein is included to explain the context of the invention. This is not to be taken as an admission that any of the material referred to was published, known or part of the common general knowledge at the priority date of any of the claims.
Some processes of preparing ophthalmic lenses start with the selection of an unfinished or semi-finished lens blank. Typically a semi-finished lens blank has a finished surface and an unfinished surface.
At least one of the surfaces of the lens blank has to be adapted so as to generate the required corrective prescription.
By machining the unfinished surface of the lens blank, the required corrective prescription can be generated.
Thereafter, the surface having been machined is polished and the peripheral edge of the thus processed lens blank is provided with a final desired contour thereby establishing a finished optical or ophthalmic lens.
According to other processing methods, the finished ophthalmic lens can be directly processed from a lens blank by machining both surfaces of the optical lens blank.
The progress made in the lens manufacturing process allows producing ophthalmic lenses that have complex designs on two optical surfaces, for example the front and back surfaces of an ophthalmic lens.
One of the difficulties when manufacturing ophthalmic lenses having at least two complex surfaces is to guaranty an accurate position of both complex surfaces relative to each other, especially when these two surfaces are progressive or regressive surfaces. Indeed, the complex designs being usually asymmetry, the relative positions of these two surfaces are very important.
Guarantying an accurate position of the two complex surfaces is complex and requires modifying the lens manufacturing process.